Defect excavation and repair
On site, electric grinding wheel is used to eliminate defects, and the metal luster is exposed within 20 mm of the surface and periphery of the defects, and the root should be smooth transition, so as to avoid the existence of dead corner which is difficult to weld through; magnetic particle inspection is carried out for the defects to confirm that there are no defects. In order to eliminate the hidden danger completely and ensure the safe operation of the unit, hot welding process was adopted on site for repair welding.
The welder has obtained the corresponding welding qualification according to DL / T 679-2012. Before welding, the welder shall carry out the simulation exercise which is suitable for the actual conditions on site and pass the inspection. The construction personnel must be familiar with the construction site and equipment, fully understand the construction content, be familiar with the welding technical specifications and acceptance standards, and go through the technical disclosure before taking up the post.
The data show that the homogeneous repair welding has the characteristics of uniform heating of the whole valve body, uniform microstructure after welding, small welding stress in the repair welding area, complete transformation of microstructure, and stable mechanical properties in the welding area, which is of great significance to prevent cracks and other defects. In order to eliminate the hidden danger completely and ensure the safe operation of the unit, the homogeneous hot welding process is adopted. The welding material grade is tgs-9cb, the specification is 3.2 mm, and the baking temperature of the welding rod is (325 ~ 375) ℃ / h. During the field welding, the welding rod is stored in the heat preservation cylinder one by one, and the temperature is maintained at (100 ~ 150) ℃.
In order to ensure welding quality and facilitate operation, it is necessary to use as little filler metal as possible to reduce welding stress and deformation. The surface of the valve body shall be 10-15 mm away from the edge of the groove, and the metal luster shall be polished. Rust, dirt, oil and other impurities are strictly prohibited. The groove surface shall be free of cracks, double skin and other defects.